1. Field of the Invention
The present invention relates to a bearing having a valve seat for a rotary compressor and, in particular, a rotary compressor bearing consisting of specific austenitic cast iron.
2. Description of the Related Art
For example, a vertical type rotary compressor has a cylinder with a main bearing fixed on an upper side and a sub-bearing fixed on a lower side thereof. An exhaust outlet extends through the main bearing in an up and down direction and a valve seat is formed at an upper surface of the main bearing which is situated near an opening of the exhaust outlet. An exhaust valve and valve stopper are located over the valve seat. A shaft is journaled in the main bearing and sub-bearing to rotate, for example, in a counter-clockwise direction and extends through the bearings and cylinder. An eccentric member is formed integral with a shaft portion defined within the cylinder such that it is biased. A rotor is mounted on the eccentric member. A suction inlet and blade groove are opened in the side wall of the cylinder. The blade is inserted in a horizontal direction through the blade groove and the upper and lower surfaces of the blade are in slide contact with the main bearing and sub-bearing. The blade is spring-urged in the horizontal direction such that a front surface of the blade is normally in slide contact with the rotor which is situated within the cylinder. By so doing, a spacing between the cylinder and the rotor is separated into a low pressure space and high pressure space.
In the operation of the aforementioned rotary compressor, the exhaust valve is moved up and down relative to the valve seat due to high and low pressure in a space between the cylinder and the rotor. For that reason, a noise corresponding to an inherent frequency of the main bearing is generated by an energy which is induced due to an impact of the exhaust valve upon the valve seat.
A bearing incorporated into the rotary compressor, and in particular, a main bearing having a valve seat is conventionally made of pearlitic cast iron with graphite crystallized in a pearlite matrix. Since, however, the main bearing made of pearlitic cast iron is low in specific damping capacity (SDC), it is not possible to effectively reduce noise which is generated due to an impact of the exhaust valve upon the valve seat upon the up and down movement of the exhaust valve.
Shinichi ENOMOTO "Iron-Nickel Alloy"(Low Expansion Alloy) was published, by a corporation (shadan-hojin) "Sheiki-Gakkai"(transliterated), as a separate volume regarding "austenitic cast iron"pp. 943 to 947, vol. 51, No. 5, May 5, 1985. This document discloses NOBINITE cast iron with graphite crystallized in great amount in an austenite matrix consisting of 2.45% of C, 1.94% of Si, 1.02% of Mn, 35.54% of Ni, 2.10% of Co and a balance of Fe, all of which are percent by weight. The NOBINITE cast iron has the properties of being high in damping capacity and better in castability and workability and can be applied to, for example, the bed, table and frame of machines, but never satisfies the wear resistance.